The present invention relates to a measuring system and method for patterns of, for example, a semiconductor wafer.
Semiconductor devices up to the present have been subjected to shrinkage, high integration, and the like in order to enlarge capacity of memory and reduce bit cost. Recently, high level of integration has been highly required, and development and production of devices having three-dimensional structures for substituting the miniaturization have been developed.
Changing a planar structure to a three-dimensional structure tends to cause the whole device to be thick. In association with this, a ratio (aspect ratio) of a hole and/or a trench tends to increase during a process to form the hole, the trench, and/or the like as stacked layers of films increases in a structure of, for example, a 3D-NAND and a DRAM,
For example, in order to know a three-dimensional shape of the hole and/or the trench having a considerably high aspect ratio with, for example, a hole diameter of 50 nm to 100 nm and a depth of 3 μm or more, an accurate cross-sectional shape can be obtained by cutting off a wafer and measuring the cross-sectional. However, in order to examine a uniformity over a wafer, it involves a labor and a cost. Therefore, besides a top dimension and a bottom dimension of the hole, a method for non-destructively measuring a cross-sectional shape or a three-dimensional of a pattern with high accuracy is necessary.
Here, typical methods to observe the three-dimensional shape without cutting-off the wafer but with an electron microscope, for example, are roughly classified into two methods, a stereoscopic observation and a top-down observation.
For example, a stereoscopic observation described in Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-517199 inclines a sample stage or an electron beam to change a relative incidence angle of the electron beam to a sample, and thus, shape measurements of, for example, a height of a pattern and an inclination angle of a sidewall are performed using a plurality of images different from an irradiation from a top surface.
Japanese Unexamined Patent Application Publication No. 2015-106530 is not effective in measuring a dimension of a bottom of a hole because detection efficiency of secondary electrons (SE, usually its energy is roughly defined to be less than 50 eV) emitted from a bottom portion decreases as an aspect ratio of a deep hole and/or a deep trench increases. Meanwhile, backscattered electrons (also referred to backscattered electrons (BSE). Usually its energy is roughly defined to be more than 50 eV) generated by primary electrons with high energy has relatively high intensity when coming out of the bottom of the hole to a sample surface, compared with the secondary electrons. Accordingly, it is effective in measuring high aspect ratio features, and therefore, there is described a method for measuring a depth of the bottom of the hole by using a phenomenon that an amount of BSE signal decreases as the hole gets deep.
A pattern with a high aspect ratio is difficult to control shapes of a sidewall and/or a bottom portion of a hole and/or a trench, and this possibly causes shapes of taper, bowing, and twisting. Therefore, not only dimensions of upper portions and lower portions of a hole and/or a trench, but also a cross-sectional shape are considered to be an important evaluation item. A uniformity over a wafer is highly required. Therefore, inspecting and measuring a uniformity, and then, feeding back to a manufacturing process of a semiconductor (for example, etching device) are the key to improve a yield.
However, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-517199 requires a measurement at a plurality of angles, and therefore, there lies a problem of, for example, an increased measurement period and/or a complicated analysis method. Moreover, since information only on edges (ends) of the pattern is obtained, a continuous three-dimensional shape cannot be measured.
Japanese Unexamined Patent Application Publication No. 2015-106530 discloses measuring a height of a bottom portion of a trench and/or a hole using a standard sample and/or measurement data whose hole depth is already known as a criteria.
That is, while Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2003-517199 and Japanese Unexamined Patent Application Publication No. 2015-106530 describe methods for observing and/or measuring a sample in a three-dimensional structure, a solution for a deterioration in a measurement accuracy caused by a relative height and/or a continuous three-dimensional shape of an identical hole, and an intensity distribution of a primary electron beam is not considered. The primary electron beam in a scanning electron microscope has a limited convergence angle, and thus, the intensity distribution of a primary beam in a lateral direction varies with a height relative to its focal position. In particular, it is found by an experiment by the inventors that in the case of a deep hole and/or a deep trench, this effect becomes remarkable, and thus, electrons generated from a top surface, a bottom surface, and a sidewall are impossible to distinguish.